Near infrared reflective multilayer material sheet

Abstract

The present invention relates to a multilayer material sheet, which comprises a NIR-reflective semi-transparent polymer layer and a NIR-reflective colored polymer layer, wherein the NIR-reflective semi-transparent polymer layer has a reflectivity of more than 20% for all light with a wavelength of 750nm to 1000nm and a transmittance of more than 50% for all light with a wavelength of 380nm to 750nm, and the NIR-reflective colored polymer layer has a reflectivity of more than 25% for all light with a wavelength of 1000nm to 2100nm. The present invention also relates to a back sheet suitable for use in a photovoltaic module, the back sheet comprising the multilayer material sheet; and to a photovoltaic module comprising the back sheet.

Description

[0001] The present invention relates to a near infrared (NIR) reflective multilayer material sheet. The present invention also relates to a back sheet suitable for a photovoltaic module comprising the NIR-reflective multilayer material sheet; and a photovoltaic module comprising the back sheet.

[0002] Photovoltaic modules are used to generate electricity from sunlight and are usually composed of laminates that contain a solar cell system as a core layer. In order to form a photovoltaic module, photovoltaic cells grouped in series using metal conductors called "ribbons" are typically encapsulated by an encapsulation material such as EVA. The encapsulation material surrounding the photovoltaic cell is used as protection against mechanical and climate-related effects. The core layer is present between the surface layer and the base layer or back sheet to complete the photovoltaic module. The surface layer or main surface of the module (usually made of glass) covers the surface of the module exposed to sunlight and allows sunlight to reach the battery. The base layer or back sheet performs a variety of tasks. It ensures that the encapsulation material and solar cells are not affected by the environment and prevents oxidation of the electrical connection. The back sheet can also enhance the power output of the module by reflecting light toward the solar cell through the front glass. Typically, depending on atmospheric conditions, the back sheet prevents moisture, oxygen and other factors from damaging the encapsulation material, solar cells and electrical connections. The back sheet also provides electrical insulation for photovoltaic cells and corresponding circuits.

[0003] Photovoltaic modules are traditionally installed outdoors on rooftops or in open areas where they are exposed to sunlight to the maximum extent possible. When the intensity of sunlight increases, the electrical output of the photovoltaic module also increases. However, the efficiency of photovoltaic modules in converting sunlight into electrical energy is generally about 20%. The remaining 80% of the sunlight is reflected back or absorbed by the module as heat. The energy absorbed in the form of heat causes the operating temperature of the module to increase. Excessive heat reduces the efficiency of the photovoltaic module in converting sunlight into electrical energy. The typical operating temperature of most photovoltaic modules is about 40-60°C. With each degree Celsius increase in operating temperature, many photovoltaic modules lose about 0.3-0.5% of efficiency. A variety of factors can cause the operating temperature to increase, such as higher ambient air temperatures during the day, radiant heat from the ground and other nearby surfaces (which may emit heat generated by exposure to sunlight), and the temperature increase of the solar module itself due to long-term exposure to sunlight.

[0004] This problem often occurs when photovoltaic modules are integrated into architectural structures containing, for example, a black backsheet for aesthetic reasons. Although the rectangular photovoltaic cells in a photovoltaic module are usually very close together, there are usually small gaps between them, exposing the underlying backsheet to sunlight. Up to 10% to 15% of the total area of ​​the backsheet covered by a typical monocrystalline silicon photovoltaic module containing 60 or 72 cells is exposed to direct sunlight.

[0005] In the case of integrating photovoltaic modules into building structures, their backsheets are usually colored, especially dark (e.g., black) to blend the photovoltaic modules with the existing building colors and provide a more uniform appearance. The colored, especially dark (e.g., black) appearance of the backsheet is usually produced by coating the backsheet with pigments (e.g., carbon black or iron oxide) or mixing these pigments with the polymer used to generate the backsheet during the backsheet manufacturing process. Carbon black absorbs essentially all light visible to humans. In addition, carbon black also absorbs infrared light, which is electromagnetic radiation with a wavelength longer than the wavelength of light that is generally visible to humans (i.e., the wavelength range is from about 750 nm to about 1 mm at the edge of visible red light). The absorption of infrared light will increase the temperature of the backsheet and ultimately increase the operating temperature of the entire photovoltaic module. Unlike black pigments (such as carbon black), pigments with an all-white appearance reflect the light visible to humans the most, and therefore absorb very little light visible to humans, and they also reflect most of the infrared light. Therefore, although dark or even black backsheets in photovoltaic modules are desirable for aesthetic reasons, such backsheets tend to increase the operating temperature of the photovoltaic module. This reduces the efficiency of the photovoltaic module in converting sunlight into electricity. In addition, the black backsheet also absorbs IR and visible light, which further reduces the overall efficiency of the photovoltaic module.

[0006] Photovoltaic module backsheets containing NIR-reflective pigments are known. For example, US2013 / 276876 describes a backsheet for a photovoltaic module, which contains a black (low color reflectivity) infrared reflective layer. Optionally, it can have a white layer as the back side. In addition, EP2860764 describes a backsheet having a black but NIR-transmitting first layer (front layer) and a NIR-reflecting second layer (rear layer).

[0007] However, there is still a need to optimize the operating temperature and efficiency of photovoltaic modules containing black backsheets.

[0008] It is therefore an object of the present invention to provide a NIR-reflective multilayer backsheet which reduces the absorption of NIR light in the backsheet.

[0009] Another object of the present invention is to provide a NIR-reflective multilayer backsheet which, when applied in a PV (photovoltaic) module, will increase module efficiency by increasing light absorption in the solar cells and reducing operating temperature.

[0010] This object has been achieved by providing a multilayer material sheet comprising a NIR-reflective semi-transparent polymer layer and a NIR-reflective colored polymer layer, wherein the NIR-reflective semi-transparent polymer layer has a reflectivity of more than 20% for all light with a wavelength of 750nm to 1000nm and a transmittance of more than 50% for all light with a wavelength of 380nm to 750nm, and the NIR-reflective colored polymer layer has a reflectivity of more than 25% for all light with a wavelength of 1000nm to 2100nm. Preferably, the reflectivity of the NIR-reflective colored polymer layer for all light with a wavelength of 380nm to 750nm is less than 35%.

[0011] In general, electromagnetic radiation is classified according to its wavelength as radio waves, microwaves, infrared light, visible light, ultraviolet light, X-rays and gamma rays. Light visible to the human eye is electromagnetic radiation with a wavelength in the range of about 380nm to about 750nm. Near infrared (NIR) light is electromagnetic radiation with a wavelength longer than that of visible light. Traditionally, near infrared light is considered to have a wavelength in the range of about 750nm to about 2100nm. When visible light or infrared light strikes an object, the light can be reflected by the object, pass through the object (i.e., transmitted by the object) or absorbed by the object. To some extent, the color of an object perceived by the human eye depends on the wavelength of the visible light that strikes the object and the wavelength of the visible light reflected by the object into the human eye.

[0012] Surprisingly it has been found that by providing a multilayer material sheet comprising a NIR-reflective translucent polymer layer and a NIR-reflective colored polymer layer, the reflection of near infrared light can be enhanced.

[0013] In the context of the present invention, translucent means semi-transparent to visible light.

[0014] In the context of the present invention, the term "colored" includes black. Thus, the term "NIR-reflective colored polymer layer" includes a NIR-reflective black polymer layer. The colored is most preferably black.

[0015] As used herein, unless otherwise stated, transmittance is measured by using an integrating sphere apparatus according to ISO 13468-2 with a sample thickness of 100 μm.

[0016] As used herein, unless otherwise specified, reflectivity is measured by a method based on ISO 13468-2 using an integrating sphere apparatus with a sample thickness of 100 μm.

[0017] The NIR-reflective semi-transparent polymer layer preferably faces the cells and is preferably located on top of the NIR-reflective colored layer. The advantage of the NIR-reflective semi-transparent polymer layer on top of the colored layer is to improve the performance of the backsheet, thereby providing increased power output, reduced built-up heat, while maintaining a colored appearance. Due to its NIR-reflective properties, the introduction of the NIR-reflective semi-transparent polymer layer increases the total reflected light in the near infrared (NIR) range (750nm-1000nm), which in turn will increase the total power output of the PV cell and reduce heat build-up. For example, the relative gain in power output of the PV module (measured according to IEC 61215) caused by the introduction of a NIR-reflective transparent layer on top of the NIR-reflective black layer in the backsheet can be greater than 0.2%, more preferably greater than 0.5%, even more preferably greater than 1.0%, compared to a non-NIR-reflective black layer. This increase can vary depending on the total loading of the pigment and the thickness of the NIR-reflective layer, and depends on the design of the photovoltaic module.

[0018] The NIR-reflective semi-transparent polymer layer and the NIR-reflective colored polymer layer may be adjacent to each other. It is also possible that the NIR-reflective semi-transparent polymer layer and the NIR-reflective colored polymer layer may be separated by an adhesive; in other words, the polymer layers contain a connecting layer or adhesive layer in between. The NIR-reflective semi-transparent polymer layer preferably faces the battery. The NIR-reflective colored polymer layer is preferably located between the NIR-reflective semi-transparent polymer layer and the outer layer of the backplane.

[0019] The NIR-reflective semi-transparent polymer layer preferably comprises one or more inorganic near-infrared reflective pigments. The inorganic near-infrared reflective pigment is selected from mica, SiO2, TiO2, tin oxide (SnO or SnO2), ZnO, ZnSnO, aluminum-doped ZnO, indium tin oxide, antimony tin oxide, ZrO2, iron oxide black Fe3O4 (magnetite), chromium oxide green Cr2O3 or chromium iron brown (Fe, Cr)2O3 and mixtures thereof. Preferably, the inorganic near-infrared reflective pigment is selected from the group consisting of mica, SiO2, TiO2, tin oxide (SnO or SnO2), ZnO, ZnSnO, aluminum-doped ZnO, indium tin oxide, antimony tin oxide, ZrO2 and mixtures thereof. More preferably, the NIR-reflective semi-transparent polymer layer comprises a NIR reflective pigment selected from mica and SiO2. Commercially known compositions comprising suitable pigments are For example 9870. 9870 contains mica + SiO2, TiO2 (rutile), SnO2 and ZrO2. Based on the total weight of the NIR-reflective semi-transparent polymer layer, the NIR-reflective semi-transparent polymer layer may contain 0.1 wt% to 8 wt% of inorganic NIR-reflective pigments. More preferably, the NIR-reflective semi-transparent polymer layer contains 0.15 wt% to 6 wt% of inorganic NIR-reflective pigments. Still more preferably, the NIR-reflective semi-transparent polymer layer contains 0.2 wt% to 4 wt% of inorganic NIR-reflective pigments.

[0020] The NIR-reflective semi-transparent polymer layer according to the present invention is preferably a thin film layer; preferably less than 300 μm thick; it is transparent to visible light with a total transmittance of ≥50% (regular transmittance & diffuse transmittance), which is measured using an integrating sphere device according to ISO 13468-2. Preferably, the thickness is 5 to 200 μm; more preferably 10 to 150 μm; more preferably 20 to 100 μm; most preferably 30 to 80 μm. Preferably, the total transmittance is at least 60%; more preferably at least 70%, for example at least 80%, or even at least 90%.

[0021] Typically, the reflectivity of the NIR-reflective translucent polymer layer to light having a wavelength of 750 nm to 1000 nm is greater than 30%; preferably greater than 40%; more preferably greater than 50%; or even greater than 60%.

[0022] The NIR-reflective semi-transparent polymer layer preferably comprises a thermoplastic polymer. The thermoplastic polymer is typically selected from the group consisting of a polyolefin, a mixture of polyolefins, TPO or a blend of a polyolefin and a semi-crystalline polymer. The thermoplastic polymer is preferably a polyolefin or a mixture of polyolefins. The polyolefin is preferably selected from the group consisting of optionally functionalized polyethylene homopolymers or copolymers, optionally functionalized polypropylene homopolymers or (block) copolymers, cyclic olefin copolymers, polymethylpentene, thermoplastic polyolefins (TPO) or their blends.

[0023] Thermoplastic polyolefins (TPO) as described herein refer, for example, to PP / EPR type reactor blended resins (e.g. Hifax CA 10, Hifax CA 12, Hifax CA 02, Hifax CA 60 supplied by Basell) or elastomeric polypropylene (PP) resins (known under the trade names Versify 2300.01 or 2400.01, mixed with, for example, random PP copolymers) or thermoplastic vulcanizates (known under the trade name Santoprene).

[0024] Examples of functionalized polyethylene or polypropylene homopolymers or (block) copolymers are for example ethylene or propylene copolymerized with a polar comonomer selected from maleic anhydride, vinyl acetate, acrylates and methacrylates, such as methyl acrylate, ethyl acrylate, butyl acrylate or ethylhexyl acrylate. Preferably, ethylene is copolymerized with methacrylate.

[0025] Preferably, the NIR-reflective translucent polymer layer comprises functionalized polyethylene, polyethylene and optionally polypropylene.

[0026] The NIR-reflective colored polymer layer comprises a polymer material and at least one NIR-reflective pigment. The layer is also colored. Therefore, it typically comprises a colored pigment. The NIR-reflective pigment and the colored pigment may be the same. The NIR-reflective colored polymer layer preferably comprises a polymer material and at least one NIR-reflective colored pigment.

[0027] The NIR-reflective coloured polymer layer according to the present invention typically has a thickness of 50 to 600 μm; more preferably 100 to 400 μm; most preferably 200 to 300 μm.

[0028] The NIR-reflective colored polymer layer according to the present invention typically has a reflectivity of more than 40% for all light with a wavelength of 1000nm to 2100nm. More preferably, the reflectivity of all light with a wavelength of 1000nm to 2100nm exceeds 50%, exceeds 60% or even exceeds 70%. The NIR-reflective colored polymer layer according to the present invention typically has a reflectivity of more than 40% for all light with a wavelength of 1200nm to 1600nm. More preferably, the reflectivity of all light with a wavelength of 1200nm to 1600nm exceeds 50%, exceeds 60%, exceeds 70% or even exceeds 80%.

[0029] The polymer material of the NIR-reflective colored polymer layer is preferably a thermoplastic polymer. The thermoplastic polymer is selected from the group consisting of polyolefins, functionalized polyolefins, polyesters, polyamides, rubber-modified polyesters, PMMA, PEEK, polycarbonates, polyethersulfones, polyoxymethylenes, polyimides, polyphenylene sulfides or polyphenylene oxides. Preferably, the thermoplastic polymer of the NIR-reflective colored polymer layer is selected from the group consisting of polyamides, polyesters, rubber-modified polyesters, polyolefins and combinations thereof.

[0030] Examples of polyolefins are polyolefin or polypropylene homopolymers or (block) copolymers. Preferably, the polyolefin is polypropylene.

[0031] Examples of functionalized polyolefins are functionalized polyethylene or polypropylene homopolymers or (block) copolymers, such as ethylene or propylene copolymerized with a polar comonomer selected from maleic anhydride, vinyl acetate, acrylates and methacrylates, such as methyl acrylate, ethyl acrylate, butyl acrylate or ethylhexyl acrylate. Preferably, the functionalized polyolefin is propylene copolymerized with maleic anhydride.

[0032] Examples of polyesters include poly(trans-1,4-cyclohexylene alkane dicarboxylates) such as poly(trans-1,4-cyclohexylene succinate) and poly(trans-1,4-cyclohexylene adipate); poly(cis- or trans-1,4-cyclohexanedimethylene) alkane dicarboxylates such as poly(cis-1,4-cyclohexanedimethylene) oxalate and poly(cis-1,4-cyclohexanedimethylene) succinate; poly(alkylene terephthalates) such as polyethylene terephthalate and polybutylene terephthalate; poly(alkylene isophthalates) such as polyethylene isophthalate and polybutylene isophthalate; poly(p-phenylene alkane dicarboxylates) such as poly(p-phenylene glutarate); glutarate) and poly(p-phenylene adipate), poly(p-xylene oxalate), poly(o-xylene oxalate); poly(p-phenylenedialkylene terephthalate) terephthalates), such as poly(p-phenylenedimethylene terephthalate) and poly(p-phenylene-di-1,4-butylene terephthalate); poly(alkylene-1,2-ethylenedioxy-4,4'-dibenzoates), such as poly(ethylene-1,2ethylenedioxy-4,4'-dibenzoate), poly(tetramethylene-1,2-ethylenedioxy-4,4'-dibenzoate) and poly(hexamethylene-1,2-ethylenedioxy-4,4'-dibenzoate); poly(alkylene-4,4'-dibenzoates), such as poly(pentamethylene-4,4'-dibenzoate), poly(hexamethylene-4,4'-dibenzoate). Poly(ethylene-2,6-naphthalene dicarboxylates), such as poly(ethylene-2,6-naphthalene dicarboxylate), poly(trimethylene-2,6-naphthalene dicarboxylate), and poly(tetramethylene-2,6-naphthalene dicarboxylate); and poly(alkylene sulfonyl-4,4'-dibenzoate), such as poly(octamethylene sulfonyl-4,4'-dibenzoate), and poly(decamethylene sulfonyl-4,4'-dibenzoate). Preferred polyesters are poly(alkylene terephthalates), such as polyethylene terephthalate (PET) or polybutylene terephthalate (PBT).

[0033] The polyester may be impact modified by an elastomer comprising a functional group that chemically bonds and / or physically interacts with the polyester. The functional group is selected from the group consisting of anhydrides, acids, epoxides, silanes, isocyanates, oxazolines, thiols and / or (meth)acrylates. Preferably, the functional group is an epoxide.

[0034] The elastomer mentioned herein refers to an elastomer selected from the group consisting of EPDM, SBS, SEBS, ethylene-propylene elastomers such as EPDM, styrene-butadiene elastomers such as SBS or SEBS. The amount of functional groups chemically bonded and / or physically interacting with the polyester is preferably 0.01 to 5% by weight (based on the total weight of the impact-modified polyester).

[0035] Examples of polyamides are polyamide 6, polyamide 6,6; polyamide 4,6; polyamide 6,10; polyamide 6,12; polyamide 6,14; polyamide 6,13; polyamide 6,15; polyamide 6,16; polyamide 11; polyamide 12, polyamide 10, polyamide 9,12, polyamide 9,13, polyamide 9,14, polyamide 9,15, polyamide 6,16, polyamide 10,10, polyamide 10,12, polyamide 10,13, polyamide 10,14, Polyamide 12,10, polyamide 12,12, polyamide 12,13, polyamide 12,14, adipic acid adipamide / terephthalic acid adipamide copolyamide, terephthalic acid adipamide / isophthalic acid adipamide copolyamide, poly(adipic acid m-dimethylbenzamide), terephthalic acid adipamide / terephthalic acid 2-methylglutaramide, adipic acid adipamide / terephthalic acid adipamide / isophthalic acid adipamide copolyamide and polycaprolactam-terephthalic acid adipamide.

[0036] Preferably, the NIR-reflective colored polymer layer comprises polypropylene or propylene copolymerized with maleic anhydride.

[0037] Examples of NIR-reflecting coloured pigments are given in Table 1 below.

[0038] Table 1:

[0039]

[0040]

[0041] For dark colored layers, preferred NIR-reflecting colored pigments are chromium iron oxides, such as Sicopal Black K0095 from BASF or Shepherd black 10G996 from Shepherd.

[0042] The NIR-reflective colored polymer layer may contain 0.1 wt % to 8 wt % of the NIR-reflective colored pigment, based on the total weight of the NIR-reflective colored polymer layer. More preferably, the NIR-reflective colored polymer layer contains 0.15 wt % to 6 wt % of the NIR-reflective colored pigment. Still more preferably, the NIR-reflective colored polymer layer contains 0.2 wt % to 4 wt % of the NIR-reflective colored pigment.

[0043] The multilayer material sheet of the present invention may further comprise other polymer layers, such as one or more adhesive layers, structural reinforcement layers and / or weathering layers. Preferably, it comprises a weathering layer.

[0044] The weathering layer may comprise polyamide, PTFE, polyolefin or polyester. Examples of suitable polyolefins, polyesters or polyamides are as described above. Preferably, the weathering layer comprises polyamide 12. Alternatively, the weathering layer comprises polypropylene.

[0045] The weather-resistant layer may further comprise an inorganic filler, such as calcium carbonate, titanium dioxide, barium sulfate, mica, talc, kaolin, glass microspheres and glass fibers; or an additive, such as a UV stabilizer, a heat stabilizer or an antioxidant. More preferably, the weather-resistant layer may be colored by any colored (including black) pigment (including IR-reflective colored pigment) as shown above, or by a white pigment. Most preferably, the weather-resistant layer comprises a white pigment.

[0046] In one embodiment, the binder is a NIR-reflective colored polymer layer as defined in the present invention.

[0047] In another embodiment, the structural reinforcement layer is a NIR-reflective colored polymer layer as defined in the present invention.

[0048] In one embodiment, the multilayer material sheet comprises the following layers:

[0049] a) a NIR-reflective semi-transparent polymer layer facing the cell,

[0050] b) an adhesive polymer layer comprising NIR-reflective pigments having a specific color including black,

[0051] c) a structural polymer layer,

[0052] d) an adhesive polymer layer, which may be the same as or different from layer (b),

[0053] e) A polymer layer or weathering layer on the air-facing side.

[0054] In this embodiment, layer a) and layer b) comprise the ingredients described above. This means that the adhesive layer is a NIR-reflective colored polymer layer as described above.

[0055] The structural layer c) comprises, for example, a thermoplastic polymer, such as a polyolefin or a mixture of polyolefins, such as polypropylene or a mixture of polypropylenes; a polyester (such as PET or PBT), which is optionally rubber-modified; or a polyamide. Optionally, the structural layer may contain NIR-reflective colored pigments, such as chromium iron oxide, more specifically Sicopal Black K0095 from BasF or Shepherd black 10G996 from Shepherd.

[0056] The polyester (e.g. PET or PBT) may be impact modified by an elastomer comprising a functional group that chemically bonds and / or physically interacts with the polyester. The functional group is selected from the group consisting of anhydrides, acids, epoxides, silanes, isocyanates, oxazolines, thiols and / or (meth)acrylates. Preferably, the functional group is an epoxide.

[0057] The elastomer mentioned herein refers to an elastomer selected from the group consisting of EPDM, SBS, SEBS, ethylene-propylene elastomers such as EPDM, styrene-butadiene elastomers such as SBS or SEBS. The amount of functional groups chemically bonded and / or physically interacting with the polyester is preferably 0.01 to 5% by weight (based on the total weight of the impact-modified polyester).

[0058] Examples of polyamides are polyamide 6; polyamide 6,6; polyamide 4,6; polyamide 6,10; polyamide 6,12; polyamide 6,14; polyamide 6,13; polyamide 6,15; polyamide 6,16; polyamide 11; polyamide 12, polyamide 10, polyamide 9,12, polyamide 9,13, polyamide 9,14, polyamide 9,15, polyamide 6,16, polyamide 10,10, polyamide 10,12, polyamide 10,13, polyamide 10,14, Polyamide 12,10, polyamide 12,12, polyamide 12,13, polyamide 12,14, adipic acid adipamide / terephthalic acid adipamide copolyamide, terephthalic acid adipamide / isophthalic acid adipamide copolyamide, poly(adipic acid m-dimethylbenzamide), terephthalic acid adipamide / terephthalic acid 2-methylglutaramide, adipic acid adipamide / terephthalic acid adipamide / isophthalic acid adipamide copolyamide and polycaprolactam-terephthalic acid adipamide.

[0059] The polymer layer or weathering layer e) on the air-facing side of the outer side of the back sheet can contain polyamide, PTFE, polyolefin or polyester. Examples of polyolefin, polyester or polyamide are as described above. Preferably, the weathering layer e) contains polyamide 12. Alternatively, the weathering layer contains a polyolefin, such as polypropylene.

[0060] The weather-resistant layer e) may further comprise an inorganic filler, such as calcium carbonate, titanium dioxide, barium sulfate, mica, talc, kaolin, glass microspheres and glass fibers; or an additive, such as a UV stabilizer, a heat stabilizer or an antioxidant. More preferably, the weather-resistant layer may be colored by any NIR-reflective pigment shown above, or by a white pigment. Most preferably, the weather-resistant layer comprises a white pigment.

[0061] In another embodiment, the multi-layer backsheet may include the following layers:

[0062] a) a NIR-reflective semi-transparent polymer layer facing the cell,

[0063] b) an adhesive polymer layer comprising NIR-reflective pigments having a specific color including black,

[0064] c) A structured polymer layer comprising NIR-reflective pigments of specific colors (including black)

[0065] d) an adhesive polymer layer, which may be the same as or different from layer (b),

[0066] e) A polymer layer or weathering layer on the air-facing side.

[0067] In this embodiment, it is possible that both adhesive layers contain NIR-reflective pigments of a specific color, including black. Layers a) to e) contain the ingredients described above.

[0068] In another embodiment, the multi-layer backsheet may include the following layers:

[0069] a) a NIR-reflective semi-transparent polymer layer facing the cell, comprising a NIR-reflective pigment selected from the group consisting of mica, SiO2, TiO2, tin oxide, ZnO, ZnSnO, aluminum-doped ZnO, indium tin oxide, antimony tin oxide, ZrO2 or mixtures thereof,

[0070] b) a binder polymer layer comprising a NIR-reflective pigment selected from the group consisting of mica, SiO2, TiO2, tin oxide, ZnO, ZnSnO, aluminum-doped ZnO, indium tin oxide, antimony tin oxide, ZrO2 or mixtures thereof, chromium iron oxide such as Sicopal Black K0095 from BASF or Shepherd black 10G996 from Shepherd,

[0071] c) a structured polymer layer comprising a NIR-reflective pigment selected from chromium iron oxides such as Sicopal Black K0095 from BASF or Shepherd black 10G996 from Shepherd,

[0072] d) an adhesive polymer layer, which may be the same as or different from layer (b),

[0073] e) A polymer layer or weathering layer on the air-facing side, preferably comprising white pigments.

[0074] In this embodiment, layers a)-e) comprise the ingredients described above.

[0075] The polymer layer may further comprise additives as known in the art. Preferably, the polymer layer comprises at least one additive selected from UV stabilizers, UV absorbers, antioxidants, heat stabilizers and / or hydrolysis stabilizers. When such additive stabilizers are present, the polymer layer may comprise 0.05 to 10 wt % additive, more preferably 1 to 5 wt % additive, based on the total weight of the polymer.

[0076] White pigments such as talc, mica, TiO2, ZnO or ZnS may also be added.

[0077] In another embodiment, the multi-layer backsheet may include the following layers:

[0078] a) a NIR-reflective semi-transparent polymer layer facing the cell, comprising a NIR-reflective pigment selected from the group consisting of mica, SiO2, TiO2, tin oxide, ZnO, ZnSnO, aluminum-doped ZnO, indium tin oxide, antimony tin oxide, ZrO2 or mixtures thereof,

[0079] b) an adhesive polymer layer comprising a NIR-reflective pigment selected from chromium iron oxides such as Sicopal Black K0095 from BASF or Shepherd black 10G996 from Shepherd,

[0080] c) a structured polymer layer comprising a NIR-reflective pigment selected from chromium iron oxides such as Sicopal Black K0095 from BASF or Shepherd black 10G996 from Shepherd

[0081] d) an adhesive polymer layer, which may be the same as or different from layer (b),

[0082] e) A polymer layer or weathering layer on the air-facing side, preferably comprising white pigments.

[0083] In this embodiment, layers a) to e) comprise polymeric materials and possible additives as described above.

[0084] In one embodiment, the present invention provides a multilayer material sheet comprising:

[0085] a) a NIR-reflective semi-transparent polymer layer comprising functionalized polyethylene, polyethylene and optionally polypropylene and NIR-reflective pigments;

[0086] b) a NIR-reflective colored layer comprising a polyolefin, a NIR-reflective pigment and a colored pigment; and

[0087] c) Weathering layer.

[0088] Typically, the multilayer material sheet further comprises a weathering layer (c), which comprises a polyolefin or a polyamide. The polyolefin and polyamide are as defined herein.

[0089] Typically, the NIR-reflective semi-transparent polymer layer comprises ethylene copolymerized with methacrylate. Typically, the NIR-reflective pigment of the NIR-reflective semi-transparent polymer layer (a) comprises mica, SiO2 or both. Typically, the amount of the NIR-reflective pigment of the NIR-reflective semi-transparent polymer layer (a) is 0.1 to 8 wt %, based on the total weight of the NIR-reflective semi-transparent polymer layer. Typically, the thickness of the NIR-reflective semi-transparent polymer layer (a) is 10 to 150 μm.

[0090] Typically, the NIR-reflective colored layer comprises polypropylene or propylene copolymerized with maleic anhydride. Typically, in the NIR-reflective colored layer (b), the NIR-reflective pigment is also a colored pigment. Typically, in the NIR-reflective colored layer (b), the NIR-reflective pigment is present in an amount of 0.1 to 8 wt % based on the gross weight of the layer. Typically, the thickness of the NIR-reflective colored layer (b) is 100 to 400 μm. Typically, the color is black.

[0091] Typically, the weathering layer comprises polyamide 12 or polypropylene. Typically, the weathering layer has a thickness of 10 to 50 μm. Typically, the weathering layer comprises a white pigment.

[0092] A particularly preferred embodiment is a multilayer material sheet as described above, wherein:

[0093] a) a NIR-reflective semitransparent polymer layer having a thickness of 10 to 150 μm, comprising ethylene copolymerized with methacrylate, and 0.1 to 8 wt. % of a NIR-reflective pigment comprising mica and SiO2;

[0094] b) the NIR-reflective colored layer (b) has a thickness of 100 to 400 μm, comprises polypropylene or propylene copolymerized with maleic anhydride, and 0.1 to 8 wt. % of a NIR-reflective pigment which is also a colored pigment; and

[0095] c) The weather-resistant layer comprises polyamide 12 or polypropylene.

[0096] The multilayer material sheet according to the present invention can be prepared using a multilayer melt or coextrusion process. The process comprises the steps of mixing individual formulations of different layers including inorganic fillers, additives and stabilizers, then extruding the different layers and laminating them.

[0097] Alternatively, the multilayer material sheet according to the present invention can also be manufactured by the following steps: (1) granulating materials of different layers in an extruder to obtain granules or pellets of different layers, and (2) melting and co-extruding the pellets or granules prepared in step (1) through an extruder. Alternatively, the multilayer material sheet can also be obtained by melt co-extruding different layers in the multilayer material sheet by the following steps: (1) preparing polymer compositions of different layers by mixing components of different layers separately, (2) melting different polymer compositions to obtain different melt streams, (3) merging the melt streams by co-extrusion in one extrusion die, and (4) cooling the co-extruded layers.

[0098] The present invention also provides a backsheet suitable for use in a photovoltaic module, the backsheet comprising a sheet of multilayer material as defined herein. Typically, the sheet of multilayer material is suitable for use as a backsheet in a photovoltaic module. Typically, the sheet of multilayer material is simply cut to size to produce the backsheet. Thus, preferably, the sheet of multilayer material is a backsheet suitable for use in a photovoltaic module.

[0099] When used as a backsheet, the NIR-reflective semi-transparent layer is oriented towards the front side (ie towards the solar cells) and the NIR-reflective colored layer is oriented towards the back side (ie away from the solar cells).

[0100] The present invention also relates to a photovoltaic module comprising a multilayer material sheet (or backsheet) according to the present invention. The photovoltaic module comprises at least the following layers in the order of position from the front side facing the sun to the back side facing away from the sun: (1) a transparent front sheet, (2) optionally a front encapsulation material layer, (3) a solar cell layer, (4) optionally a back encapsulation material layer and (5) a multilayer backsheet according to the present invention, representing the back protective layer of the PV module.

[0101] Typically, the front pane is a glass sheet.

[0102] Front encapsulation materials and back encapsulation materials are designed to seal and protect fragile solar cells. The "front side" corresponds to the side of the photovoltaic cell that is illuminated by light, i.e., the light receiving side, while the term "back side" corresponds to the back of the light receiving side of the photovoltaic cell. Suitable encapsulation materials generally have a combination of the following features: high impact resistance, high penetration resistance, good resistance to ultraviolet (UV) light, good long-term thermal stability, sufficient adhesion strength to glass and / or other rigid polymer sheets, high moisture resistance and good long-term weathering ability. Examples of encapsulation materials are ionomers, ethylene vinyl acetate (EVA), poly (vinyl acetal), polyvinyl butyral (PVB), thermoplastic polyurethane (TPU), polyvinyl chloride (PVC), metallocene-catalyzed linear low-density polyethylene, polyolefin block elastomers, poly (ethylene-co-methyl acrylate) and poly (ethylene-co-butyl acrylate), silicone elastomers or epoxy resins. EVA is the most commonly used encapsulation material. EVA sheets are usually inserted between the solar cell and the top surface (called the front encapsulation material) and between the solar cell and the back surface (called the back encapsulation material).

[0103] The solar cells in the solar cell layer may be any kind of solar cells, such as thin film solar cells (eg, copper indium gallium selenide solar cells and cadmium telluride solar cells) and wafer-based solar cells.

[0104] The present invention also relates to a multilayer backsheet for a photovoltaic module, comprising a NIR reflective semi-transparent polymer layer and a colored polymer layer, wherein the NIR reflective semi-transparent polymer layer has a reflectivity of more than 20% for all light with a wavelength of 750nm to 1000nm and a transmittance of more than 50% for all light with a wavelength of 380nm to 750nm, and the colored polymer layer has a reflectivity of less than 35% for all light with a wavelength of 380nm to 2100nm. Preferably, the colored polymer layer comprises carbon black. The NIR reflective semi-transparent polymer layer and the colored polymer layer are composed of the materials described above. The multilayer material sheet may also include at least an adhesive layer, a structural layer and a weathering layer.

[0105] Typically, the reflectivity of the colored polymer layer to all light having a wavelength of 380 nm to 2100 nm is less than 30%; more preferably less than 25%; and even more preferably less than 20%.

[0106] Typically, the total transmittance of the NIR-reflective translucent polymer layer for all light having a wavelength of 380 nm to 750 nm is at least 60%, preferably at least 70%; more preferably at least 80%, such as at least 90%.

[0107] Typically, the reflectivity of the NIR-reflective translucent polymer layer to light having a wavelength of 750 nm to 1000 nm is more than 30%; preferably more than 40%; more preferably more than 50%; or even more than 60%.

[0108] In a preferred embodiment, the multilayer backsheet comprises the following layers:

[0109] a) a NIR-reflective semi-transparent polymer layer facing the cell, comprising a NIR-reflective pigment selected from the group consisting of mica, SiO2, TiO2, tin oxide, ZnO, ZnSnO, aluminum-doped ZnO, indium tin oxide, antimony tin oxide, ZrO2 or mixtures thereof,

[0110] b) a binder polymer layer comprising a NIR-reflective pigment selected from the group consisting of mica, SiO2, TiO2, tin oxide, ZnO, ZnSnO, aluminum-doped ZnO, indium tin oxide, antimony tin oxide, ZrO2 or mixtures thereof, chromium iron oxide such as Sicopal Black K0095 from BASF or Shepherd black 10G996 from Shepherd,

[0111] c) a structural polymer layer comprising carbon black,

[0112] d) an adhesive polymer layer, which may be the same as or different from layer (b),

[0113] e) A polymer layer or weathering layer on the air-facing side, preferably comprising white pigments.

[0114] In an even more preferred embodiment, the multilayer backsheet comprises the following layers:

[0115] a) a NIR-reflective semi-transparent polymer layer facing the cell, comprising a NIR-reflective pigment selected from the group consisting of mica, SiO2, TiO2, tin oxide, ZnO, ZnSnO, aluminum-doped ZnO, indium tin oxide, antimony tin oxide, ZrO2 or mixtures thereof,

[0116] b) a non-pigmented binder polymer layer,

[0117] c) a structural polymer layer comprising carbon black,

[0118] d) an adhesive polymer layer, which may be the same as or different from layer (b),

[0119] e) A polymer layer or weathering layer on the air-facing side, preferably comprising white pigments.

[0120] The various layers in these embodiments are preferably composed of the polymeric materials and additives described above.

[0121] The invention will be explained in further detail with the aid of figures and examples, but the invention is not restricted thereto.

[0122] Figure 1 is a graph of reflectivity versus wavelength for a film of the NIR reflective translucent polymer layer of Example 3.

[0123] Figure 2 is a graph of transmittance versus wavelength for a film of the NIR reflective translucent polymer layer of Example 3.

[0124] Figure 3 is a graph of reflectivity versus wavelength for a film of the NIR-reflective colored polymer layer of Example 4.

[0125] Figure 4 is a graph of reflectivity versus wavelength for the coextruded film of the multilayer material sheet of Example 5.

[0126] Figure 5 is a graph of reflectivity versus wavelength for the multilayer material sheets of Examples 6, 7, 8 and the coextruded film of Comparative Experiment 1.

[0127] Figure 6 is a graph of reflectivity versus wavelength for a film of the NIR-reflective colored polymer layer of Example 4.

[0128] Figure 7 is a graph of reflectivity versus wavelength for a film of the NIR-reflective colored polymer layer of Example 4.

[0129] Figure 8 An example of a multilayer material sheet according to the present invention is obtained. The functional layer (1) is connected to the structural reinforcement layer (3) via an adhesive layer (2). The weathering layer (5) is connected to the other side of the structural reinforcement layer (3) via a second adhesive layer (4).

[0130] The present invention will now be described in detail with reference to the following non-limiting examples, which are intended to be illustrative only. Example

[0131] Example 1 : Preparation of NIR-reflective translucent particles 1

[0132] The mixture was prepared in a twin-screw extruder by adding to a powder a polymer mixture of 70 wt % polyethylene and 30 wt % polyethylene copolymer containing additives. 9870 powder was used to prepare pellets of NIR-reflective translucent polymer material. The twin-screw extruder was equipped with a feeder (18 mm screw), containing elements for mixing, melting and transporting the melt, a vacuum dome, atmospheric degassing and a 1 x 4 mm die plate. A 1.5 m long water bath, an air knife and a pelletizer were installed in a continuous sequence after the die. The total concentration of 9870 was 3 wt % relative to the total weight of the polymer material. All materials were fed on the throat. The temperature of zone 1 was set to 200°C and the other zones were set to 230°C. The temperature of the melt measured when leaving the die was 270°C. The extruder was set at 300 RPM and the production capacity was 5 kg / hr. The vacuum was set to -0.7 bar.

[0133] Example 2 : Preparation of NIR-reflective black particles 2

[0134] The particles of NIR-reflective black polymer material are produced by adding ShepherdBlack BK10G966 powder to polypropylene in powder form containing additives in a twin screw extruder equipped with a feeder (18 mm screw), comprising elements for mixing, melting and transporting the melt, a vacuum dome, atmospheric degassing and a 1 x 4 mm die plate. A 1.5 m long water bath, an air knife and a pelletizer are installed in a continuous order after the die. The total concentration of ShepherdBlack BK10G966 in the mixture is 8 wt % relative to the total weight of the polymer material. All materials are fed on the feeding port (throat). The temperature of zone 1 is set to 200 ° C, and the other zones are set to 230 ° C. The temperature of the melt measured when leaving the die is 270 ° C. The extruder is set at 300 RPM, and the production capacity is 5 kg / hr. The vacuum is set to -0.7 bar.

[0135] Example 3 : Film processing of NIR-reflective translucent particles 1

[0136] Pellets 1 (Example 1) were processed into cast films with a thickness of about 20 μm using a Collin flat wire machine equipped with a single screw extruder 30 / 25D (with 3-stage screw), a feeder, a 300 x 0.4 mm flat coating die and a take-off device. The barrel temperature started with water cooling at the inlet until the end of 225°C. The connector, feeder and die temperature were set to till 225°C. The take-off speed was 5 m / min. The screw speed was 15 RPM.

[0137] The total reflectance and total transmittance of the film were measured at a thickness of 20 μm using an integrating sphere device based on ISO 13468-2 and are shown in Figure 1 and Figure 2 middle.

[0138] Example 4 : Film processing of NIR-reflective black particles 2

[0139] Pellets 2 (Example 2) were processed into a cast film with a thickness of about 150 μm using a Collin flat wire machine equipped with a single screw extruder 30 / 25D (with a 3-stage screw), a feeder, a 300 x 0.4 mm flat coating die and a take-off device. The barrel temperature started with water cooling at the inlet until the final 225°C. The connector, feeder and die temperatures were set to a maximum of 225°C. The take-off speed was 3 m / min. The screw speed was 60 RPM. The total reflectivity of the film was determined based on ISO 13468-2 at a thickness of 150 μm using an integrating sphere device and is shown in Figure 3 middle.

[0140] Example 5 :NIR-reflective multilayer backsheet

[0141] Pellets 1 and 2 were coextruded into a multilayer cast film of 170 μm thickness using a Collin flat film line with a multilayer setting of 2 extruders. Extruder A is a single screw extruder 30 / 25D with a 3-stage screw. Extruder B is a single screw extruder 25 / 25D also with a 3-stage screw. It is further equipped with a feeder 2-layer setting, a flat coating die 300x0.4mm and a take-off device. The barrel temperature is changed from water cooled at the inlet until the last 225°C. The connector, feeder and die temperature are set to till 225°C. The take-off speed is 3m / min. Pellets 2 are fed to extruder A, and the screw speed is 60RPM, which gives a thickness of 150μm. Pellets 1 are fed to extruder B, and the screw speed is 16RPM, which gives a thickness of 20μm. With the NIR-reflective semi-transparent layer facing the light source, the total reflectance of the film was measured based on ISO 13468-2 at a thickness of 170 μm using an integrating sphere apparatus and is shown in Figure 4 middle.

[0142] Examples 6 to 8

[0143] The ingredients listed in Table 1 below for each layer of each example were melt mixed and pelletized in an extruder separately together with standard additives to obtain pellets for each layer. The parts given are parts by weight, the total weight of each component being 100.

[0144] Table 1:

[0145]

[0146] For each example, the pellets were fed into one of the multiple extruders, melt-extruded at high temperature, passed through an adapter and a die, cooled by a cooling roller, and formed into a multilayer film with a total thickness of 300 μm. Each example had the following composition in order:

[0147] 30μm weather-resistant layer;

[0148] 25μm adhesive layer;

[0149] 190μm structural reinforcement layer;

[0150] 25μm adhesive layer;

[0151] ·30μm functional layer.

[0152] Comparative experiment 1: Highly reflective black backplane

[0153] A highly reflective black backplane was produced according to implementation (3) of Examples 1 and 2 of US 2013 / 276876.

[0154] With the functional polymer layer facing the light source, the total reflectance of each of Examples 6, 7, 8 and Comparative Example 1 was measured based on ISO 13468-2 and using an integrating sphere device. The results are shown in Figure 5 Examples 6, 7 and especially Example 8 give higher total reflectance in the NIR region from 750 nm to 1000 nm. Examples 6, 7 and especially Example 8 give higher total reflectance in the NIR region from 750 nm to 1000 nm. This wavelength range is the most relevant because it is above the visible spectral range of the human eye (approximately 380-740 nm) and in this range the (external) quantum efficiency of typical silicon solar cells is relatively high (>90%).

[0155] Embodiment 9: NIR-reflective green polymer layer

[0156] The strand of NIR-reflective polymer material is produced by adding Shepherd Green 10C650 powder to a powder of a polymer mixture of 70 wt % polyethylene and 30 wt % polyethylene copolymer containing additives. The mixture is introduced into a small twin-screw extruder. The total concentration of ShepherdGreen 10C650 in the mixture is 8 wt % relative to the total weight of the polymer material. The mixture is melt-extruded at 175 ° C and 200 rpm for 2 minutes, where the material is collected as a strand. A film is pressed from the strand by placing about 1 gram into a pre-cut aluminum mold having a size of 100mm x 100mm x 65 μm. Pressing is performed at 175 ° C for 3 minutes using a THB400 handheld press. The pressure is gradually increased from 100 kN to 200 kN and finally to 300 kN. Each step lasts 1 minute. After 3 minutes, the sample is cooled to room temperature under pressure. A film with a thickness of 100 μm is obtained. The total reflectance of the film was measured using an integrating sphere device based on ISO 13468-2 and is shown in Figure 6 A green film was prepared, which showed significant reflectivity at wavelengths greater than 750 nm.

[0157] Embodiment 10: NIR-reflective orange polymer layer

[0158] Example 9 was repeated except that 8 wt% Shepherd Orange 10P340 powder was used instead of 8 wt% Shepherd Green 10C650. The total reflectance of the film was measured using an integrating sphere apparatus according to ISO 13468-2 and is shown in Figure 7 An orange film was produced, which had significant reflectivity at wavelengths greater than 600 nm.

Claims

1. A multilayer material sheet comprising a NIR-reflective semi-transparent polymer layer and a NIR-reflective colored polymer layer, wherein the NIR-reflective semi-transparent polymer layer has a reflectivity of more than 20% for all light with a wavelength of 750nm to 1000nm and a transmittance of more than 50% for all light with a wavelength of 380nm to 750nm; and the NIR-reflective colored polymer layer has a reflectivity of more than 25% for all light with a wavelength of 1000nm to 2100nm, wherein the NIR-reflective semi-transparent polymer layer is located on top of the NIR-reflective colored polymer layer.

2. The multilayer material sheet of claim 1, wherein the NIR-reflective colored polymer layer has a reflectivity of less than 35% for all light having a wavelength of 380 nm to 750 nm.

3. A multilayer material sheet according to claim 1 or claim 2, wherein the NIR-reflective translucent polymer layer and the NIR-reflective colored polymer layer are adjacent to each other or separated by an adhesive layer.

4. The multilayer material sheet of claim 1, wherein the NIR-reflective translucent polymer layer comprises an inorganic near infrared reflecting pigment.

5. The multilayer material sheet according to claim 4, wherein the inorganic near-infrared reflective pigment is selected from the group consisting of mica, SiO2, TiO2, tin oxide, ZnO, ZnSnO, aluminum-doped ZnO, indium tin oxide, antimony tin oxide, ZrO2 and mixtures thereof.

6. The multilayer material sheet according to claim 4 or claim 5, wherein the NIR-reflective translucent polymer layer comprises 0.1 wt% to 8 wt% of the inorganic near-infrared reflective pigment, based on the total weight of the NIR-reflective translucent polymer layer.

7. The multilayer material sheet according to claim 1, wherein the total transmittance of the NIR-reflective semitransparent polymer layer measured according to ISO 13468-2 is ≥ 50%.

8. The multilayer material sheet of claim 1, wherein the NIR-reflective translucent polymer layer comprises a thermoplastic polymer.

9. The multilayer material sheet according to claim 8, wherein the thermoplastic polymer is a polyolefin or a mixture of polyolefins.

10. The multilayer material sheet of claim 1, wherein the NIR-reflective colored polymer layer comprises a thermoplastic polymer.

11. The multilayer material sheet of claim 10, wherein the thermoplastic polymer of the NIR-reflective colored polymer layer is selected from the group consisting of polyamides, polyesters, rubber-modified polyesters, polyolefins, and combinations thereof.

12. The multilayer material sheet of claim 1, wherein the NIR-reflective translucent polymer layer has a thickness of 10 μm to 150 μm.

13. The multilayer material sheet of claim 1, wherein the NIR-reflective colored polymer layer has a thickness of 100 μm to 400 μm.

14. The multilayer material sheet of claim 1, further comprising a weathering layer.

15. A multilayer material sheet comprising a NIR-reflective translucent polymer layer and a colored polymer layer, wherein the NIR-reflective translucent polymer layer has a reflectivity of more than 20% for all light with a wavelength of 750nm to 1000nm and a transmittance of more than 50% for all light with a wavelength of 380nm to 750nm; and the colored polymer layer has a reflectivity of less than 35% for all light with a wavelength of 380nm to 2100nm, wherein the NIR-reflective translucent polymer layer is located on top of the colored polymer layer.

16. The multilayer material sheet of claim 15, wherein the colored polymer layer comprises carbon black.

17. A multilayer material sheet comprising: a) a NIR-reflective semitransparent polymer layer, said layer comprising functionalized polyethylene, polyethylene and polypropylene and NIR-reflective pigments; b) a NIR-reflective colored layer, said layer comprising a polyolefin, a NIR-reflective pigment and a colored pigment; and c) a weathering layer, wherein the NIR-reflecting semi-transparent polymer layer is located on top of the NIR-reflecting colored layer, wherein the NIR-reflective translucent polymer layer has a reflectivity of more than 20% for all light with a wavelength of 750 nm to 1000 nm and a transmittance of more than 50% for all light with a wavelength of 380 nm to 750 nm; and The reflectivity of the NIR-reflective colored layer to all light with a wavelength of 1000 nm to 2100 nm exceeds 25%.

18. The multilayer material sheet according to claim 17, wherein: a) the NIR-reflective semitransparent polymer layer has a thickness of 10 to 150 μm and comprises ethylene copolymerized with methacrylate and 0.1 to 8 wt. % of a NIR-reflective pigment comprising mica and SiO2; b) the NIR-reflective colored layer has a thickness of 100 to 400 μm and comprises polypropylene or propylene copolymerized with maleic anhydride and 0.1 to 8 wt. % of a NIR-reflective pigment which is also a colored pigment; and c) The weather-resistant layer comprises polyamide 12 or polypropylene.

19. A backsheet suitable for use in a photovoltaic module, the backsheet comprising a sheet of multilayer material as defined in any one of claims 1 to 18.

20. A photovoltaic module comprising a backsheet as defined in claim 19.

21. The photovoltaic module according to claim 20, which comprises, in order from the sun-facing front side to the non-sun-facing back side: a transparent top layer; a front encapsulation material layer; a solar cell layer, comprising one or more electrically interconnected solar cells; a back encapsulation material layer; and a back sheet.

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